This invention relates to a crosstalk detecting apparatus for detecting crosstalk which may occur from an adjacent track when an image signal FM-modulated and recorded on a recording medium is read out.
A high-vision signal having 1,125 horizontal scanning lines per frame requires a much wider frequency band in comparison with an NTSC signal having 525 horizontal scanning lines, and specifically, a frequency band of approximately 30 MHz is necessary.
A method of recording such a wide band high-vision signal on an optical disk or the like is disclosed in Japanese Patent Application No. 2-143589, entitled "Apparatus and Recording Medium for High-Vision Signal Recording".
According to this prior art, three tracks on a recording medium are simultaneously used to accumulatively process a supplied high-vision signal which is then divided for every three consecutive scanning lines, and signals corresponding to the divided three scanning lines are recorded on the three tracks in a corresponding relationship. In other words, the simultaneous use of the three tracks causes a sweeping time to be multiplied by a factor of three, thereby recording a signal with the frequency band thereof being reduced to 1/3.
When a signal is recorded on a recording medium, a signal having a different level for each of three tracks (this signal hereinafter designates identification signal) is added to the image signal in order to identify the three different tracks upon reproducing the signal on the recording medium. Thus, during a period in which the identification signal is added, a reproduced output contains an FM wave which was generated when the identification signal was FM-modulated, and the FM wave at a different frequency is reproduced for each of the three tracks.
For thus using three tracks and reading out signals from a recording medium on which FM-modulated signals have been recorded, pickups for reading out the signals are required to perpendicularly face the tracks. Generally, for placing a pickup perpendicularly to a track, a servo system is employed which detects a displacement of the pickup from its normal perpendicularly facing position to the track and moves the pickup so as to make the displacement 0.
The present invention provides an apparatus for detecting a signal corresponding to the above-mentioned signal indicative of a displacement. In general, as described in Japanese Laid-open Utility Model Application No. 59-168835, entitled "Apparatus for Optically Reading Information," light emitted from a light emitting element and reflected by the disk surface is received by a pair of light receiving elements associated with the light emitting element, and the difference between output signals of light receiving elements is outputted as a displacement.
As described above, the difference between output signals from two light receiving elements associated with a light emitting element has been outputted as a displacement signal. For this purpose, the light emitting element and light receiving elements are required to be placed at highly precise positions, which can only be achieved by an expert. Also, even if an outputted displacement signal indicates zero, some of the signal read by a pickup may be mixed with crosstalk from an adjacent track.